Is there a way to hide/remove parts of a fluid sim mesh so they won't show in render?
In case of Particles System type Fluid, there is not a direct way to hide part of particles. You would have to convert sim to mesh.
In this example I used Metaball as particle (because Icosphere object keeps particle system after export).

export into Alembic format
import back and use Boolean Modifier




EDIT
OK I got it, you mean particles generated by Fluid Simulation (Mantaflow) - Liquid and Spray.

Yes, particles are not affected by Boolean Modifier.

So there does not exist a way to hide a part of released particles. So only way I know is to use Mball as particle and export-import it as Alembic and use Boolean.



Note: In theory - to exclude some particles from render you can influent particles size by Texture, so classic particle system can do this, but fluid sim particles doesnt have such feature.